On 10/08/2013 11:23 PM, Eric Dumazet wrote:
> On Tue, 2013-10-08 at 18:04 +0800, Gao feng wrote:
>> Though I don't face an oops, but it is more safer to
>> set table's subsys through rcu_assign_pointer.
>>
>> Signed-off-by: Gao feng <gaofeng@xxxxxxxxxxxxxx>
>> ---
>> net/netfilter/nfnetlink.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
>> index 572d87d..3cd2fe6 100644
>> --- a/net/netfilter/nfnetlink.c
>> +++ b/net/netfilter/nfnetlink.c
>> @@ -78,7 +78,7 @@ EXPORT_SYMBOL_GPL(nfnetlink_subsys_register);
>> int nfnetlink_subsys_unregister(const struct nfnetlink_subsystem *n)
>> {
>> nfnl_lock(n->subsys_id);
>> - table[n->subsys_id].subsys = NULL;
>> + rcu_assign_pointer(table[n->subsys_id].subsys, NULL);
>> nfnl_unlock(n->subsys_id);
>> synchronize_rcu();
>> return 0;
>
> Certainly not.
>
> Assigning a NULL pointer do not require rcu_assign_pointer() but this,
> if you want to be really really clean.
>
The reason assigning a NULL pointer do not require rcu_assign_pointer
is it's impossible for a reader to access to uninitialized content?
So we don't need write barrier here to make sure the resource being
initialized before reader accessing it. Right?
> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
> index 572d87d..649958b 100644
> --- a/net/netfilter/nfnetlink.c
> +++ b/net/netfilter/nfnetlink.c
> @@ -78,7 +78,7 @@ EXPORT_SYMBOL_GPL(nfnetlink_subsys_register);
> int nfnetlink_subsys_unregister(const struct nfnetlink_subsystem *n)
> {
> nfnl_lock(n->subsys_id);
> - table[n->subsys_id].subsys = NULL;
> + RCU_INIT_POINTER(table[n->subsys_id].subsys, NULL);
> nfnl_unlock(n->subsys_id);
> synchronize_rcu();
> return 0;
>
>
>
>
>
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